Bi-polar electrocautery tools have been used for a variety of electrosurgical procedures. For example, where a very controlled, localized current concentration is required, such as neuro- and eye surgery the bi-polar needle is especially useful. Currently, for these procedures, a forcep type probe is used. Each leg of the forcep is electrically isolated and insulated up to the extreme end of the tip. Only when the ends of the tip are brought into close proximity is there current flow, and then only across the gap between the tips. While this structure permits extremely accurate surgical procedures involving only minute amounts of tissue, the area of tissue burn must first be exposed to be reached with the forceps. Typically, a substantial amount of surgical cutting is required to locate the correct site for such forcep type electro-needles. Further, typical needles are expensive and not disposable, which leads to a variety of maintenance problems, including cleaning, resterilization, and maintenance of extremely delicate surgical instruments.
Applicants have developed an inexpensive bi-polar needle designed to be disposable. Bi-polar tools are not new; they have been known for some time. Typical bi-polar tools include an inner and outer electrode and an intermediate layer of epoxy. The epoxy layer tends to break down upon the above described maintenance. These bi-polar tools are exemplified by Colyer, U.S. Pat. No. 3,682,162, which includes a small diameter hypodermic needle inserted into a larger diameter hypodermic needle and bonded together with an epoxy resin or other thermosetting plastic material as an intermediate layer. The history of such bi-polar needles are summarized in Cosens et al., U.S. Pat. No. 4,034,762, which is incorporated herein by reference. Cosens et al. recognized the problem of such bi-polar needles, and created a needle which could be re-usable and withstand the rigors of maintenance. For instance, as seen in FIGS. 1 and 2 of Cosen et al., a cap 12 is required to hold the electrodes together while dielectric tubing is used to insulate the electrodes. However, even Cosens et al. uses epoxy to secure the outer electrode to the cap 12.
Applicants' structure relies upon the natural properties of elastomeric heat-recoverable materials to fix the position of the electrodes with respect to each other. Further, applicants select the elastomeric heat-recoverable material of a proper dielectric constant for correct insulation. In applicants' preferred embodiment, they use a cross-linked polymeric heat-recoverable material which can withstand the high power output which may be carried by applicants' electrodes without experiencing break down.
While cross-linked material is not new to the field of catheter manufacture, such material has not been found to be used for joining bi-polar electrodes nor for insulating the same as claimed by applicants here. For instance, Taylor, U.S. Pat. No. 4,227,293, discloses a catheter having a flexible annular balloon secured to a shaft of the catheter by a pair of annular sleeves. The annular sleeves are typically of a cross-linked material and are shrunk over the grooves of the shaft to hold the flexible annular balloon to the catheter shaft. This type of structure is clearly different from applicants' claimed structure.